Professor rashad is interested in studying cognitive development. he collects and compares data from a group of 6-year-olds and a group of 10-year-olds. five years later, he compares these two groups to each other again as well as to their own performance in the study five years ago. what type of research design is professor rashad using?

Professor Rashad is using a longitudinal research design. 

This research design involves periodically collecting data from the same participants of a study over a long period of time. Longitudinal studies are useful when investigating certain phenomena (such as cognitive development) and comparing their developments during different stages or time periods in a participant's lifespan .